Downflow forced air heating systems



C. F. SUESSEROTT DOWNFLOW FORCED AIR HEATING SYSTEMS Filed March 29,1954 FIG. 2

INVENTOR. CHARLES F. SUESSEROTT BY g, .9

HIS ATTORNEY nited States Patent DOWNFLOW FORCED AIR HEATING SYSTEMSCharles F. Suesserott, West Caldwell, N. 1., assignor to GeneralElectric Company, a corporation or New York Application March 29, 1954,Serial No. 419,338

3 Claims. (Cl. 236-11) The present invention relates to downflow forcedair heating systems or furnaces and is particularly concerned withcontrol means for controlling the operation thereof.

In downfiow furnaces and the like, the air to be heated is forced toflow over the heater in a direction which is the reverse of that whichwould be obtained by gravity circulation. For this reason the downflowfurnaces involve control problems not present in the usual heatingsystems in which the forced circulation is in the same direction as thegravity circulation. For example in the case of the switch mechanismcontrolling the operation of the air circulating blower, the heatsensing element must be located so that it senses radiant heat from theheater before air circulation is established and must not be affected bythe cold air from the blower after the forced circulation has once beenestablished. The problem is further complicated when it is desired toincorporate in one control mechanism both the fan operating means andthe limit control since the limit control must stop the burner when thedischarge air temperatures become excessive. Since forced circulation inthe downfiow furnace is the reverse of gravity circulation, two limitcontrols are frequently employed to prevent excessive temperatures offan motors, belts, bearings, heating elements and so forth. One of thelimit controls is positioned to sense the temperature of the dischargeair under forced air circulation while the second is positioned at adifferent point in the heating system for the purpose of sensingexcessive temperatures in the gravity circulated air in the event theforced air circulation system fails for any reason.

Thus it is apparent that in the usual downflow furnace at least two aircontrols, that is, a combination fan and limit control plus acounterfiow limit control, are required and in some cases a single fancontrol plus two limit controls might be necessary. Even when separatethermal elements are used for the fan control and the limit controls itis necessary or desirable that these various controls be interlock-edeither mechanically or electrically since otherwise the heating systemmay shut down due to the limit control operation before the fan controlinitiates operation of the blower.

Accordingly it is an object of the present invention to provide adownflow forced air furnace including control means operable by eitherforced or gravity air circulation.

A further object of the invention is to provide a single combination fanand limit control adapted to regulate the operation of the fan andheater independent of the direction of air travel through the heatingsystem.

Further objects and advantages of the invention will become apparent asthe following description proceeds, and the features of novelty whichcharacterize the invention will be pointed out with particularity in theclaims annexed to and forming a part of the specification.

The term downflow as applied to furnaces and heating systems may bedefined for the purposes of the present invention as covering heatingappliances in which the forced air inlet or return opening is at anelevation higher than the forced air outlet or discharge opening underwhich conditions the normal or gravity circulation of air through theappliance is in a direction opposite to that effected by the blower orother forced air circulating means.

In accordance with the present invention there is provided a downilowforced air furnace including a heater and means including a blower orother air circulating means for circulating air over the heater anddischarging the heater air into a duct system or space to be heated. Toassure satisfactory operation of the furnace under either forced orgravity air circulation, there is provided an improved control meansincluding a duct in heat exchange relationship With the air surroundingthe heater with one end of the duct in communication with the inlet tothe blower and the other end open to the heated air stream on the downstream side of the heater with reference to the direction of air travelunder forced air circulation. In the path of the air flowing through theduct and above the heater there is positioned suitable furnace controlssuch as a combination fan and limit control in which position thecontrols are subjected to the heated air which passes over the heaterunder all conditions.

For a better understanding of the invention, reference may be had to theaccompanying drawing in which:

Fig. 1 is a diagrammatic view partially in section of a verticaldownflow forced air furnace;

Fig. 2 is a view of a horizontal type furnace operating on the downflowprinciple; and

Fig. 3 is a simple wiring diagram illustrating one means of applying thecontrol system of the present invention.

In the modification of the invention shown in Fig. l, the numeral llindicates a heater or combustion chamber including a fuel burner 2 whichmay for example be a gas burner or oil burner. The products ofcombustion from the combustion chamber 1 are removed through a stack 3.Air to be heated is circulated downwardly over the heater 1 by a blower4 positioned above the heater. The blower 4 may have its outlet 5connected to the inlet end of a shell 6 surrounding the heater 1, thepurpose of the shell 6 being to confine and direct the air circulated bythe blower 4 to the immediate vicinity of the heater. The air afterbeing heated by the heater 1 is conducted downwardly to supply ducts 7.

The blower and heater are preferably enclosed in an outer casing 8having a partition 9 dividing the casing into a blower compartment lit)and a heater compartment 11. The blower compartment 16} houses theblower 4 and the blower motor 13 and is provided with an opening 12 foradmitting air to be heated to the inlet end of the blower 4.

In a furnace of this construction the normal or gravity flow circulationof air is upwardly through the furnace in the direction of the brokenarrows, and out through the inlet of the blower, the blower compartment10 and the opening 12 at the top of the blower compartment. On the otherhand when the blower 4 is in operation the air flow is reverse and takesthe direction of the solid arrows downwardly from the blower over theheater 1 and out of the bottom of the furnace into the duct system 7.Thus it is seen that any fan control of the temperature responsive typeadapted to sense the temperature of the heater 1 must of necessity be sopositioned that once it has sensed this temperature it must not again beaffected by the cold air from the blower. Likewise limit controlswitches which sense excessive heater temperatures must be positioned tosense such excessive temperatures both under forced or gravity aircirculation.

In the past safety requirements have necessitated at least two limitcontrol switches in such furnaces, one responsive to the gravity aircirculation and the other responsive to forced air circulation.

' In accordance with the present invention there is provided controlmeans requiring only a single limit control which is preferably alsocombined with the fan control. This control means comprises an openended duct 14 in heat exchange relationship with the air surrounding theheater 1. This duct may for example be connected in thermal exchangerelationship with the shell 6 if a shell is used. The duct 1- 3 is shownas extending vertically with its upper open end 15 terminating in theblower compartment above the partition 9 and its lower end terminatingat a suitable distance below the partition in air flow relationship withthe air stream which has been circulated over the heater by the blower4. A combination fan control and limit control switch is positionedadjacent the upper or outlet end of the duct 14 above the heater and inthe path of the air stream passing upwardly through the duct.

A suitable combination fan and limit control switch 17 as shown in Fig.3 comprises a bimetallic element 18 having one end fixed to a support 19and having at the other end a rod 20 provided with two arms 21 and 22.Arm 22 operates a switch 23 in the fan motor circuit, which switch isadapted to close the fan motor circuit when the thermal element 18becomes sufiiciently heated by radiation and hot air rising through theduct 14. Ann 21 operates a limit control switch 25 which is in a circuitcontrolling a solenoid operated fuel valve control 26 and is normallyclosed so that the fuel valve control solenoid holds the fuel valve inan open position. In case of excessive temperatures adjacent the heater1, which temperatures are transmitted by radiation and by the upwardlymoving air stream in ducts 14 to the thermal element 18, an arm 21engages the operating button 28 of the limit control switch so that thisswitch is opened and the solenoid valve 26 closed to cut off the supplyof fuel to the burner 2.

From the arrangement of the duct 14 it will become apparent that thethermal element 18 of the combination fan and limit control 17 is heatedby gravity air circulation upwardly through the duct 14 as a result ofradiant and convected heat from the heating element 1 before forcedcirculation is established by the operation of the blower 4. Thisinitial heating will start the furnace blower and establish the forcedcirculation. As soon as the forced circulation has been established.heated air is also drawn upwardly through the control duct 14 due to thepressure differential that has been established across the barrier 9separating the blower compartment 19 from the heating compartment 11. Inother words with the blower 4 in operation, the pressures existingwithin the blower compartment are somewhat lower than the pressuresexisting below the partition 9 and particularly below the heater 1 withthe result that part of the heated air passing over the heater 1 isdrawn into the lower end of the duct 14 and upwardly through the ductinto contact with the thermal element 18.

Should the discharge air temperatures from the furnace become excessive,the thermal element will sense this excessive temperature and the limitcontrol switch 25 will operate to shut down the burners. On the otherhand, if the blower 4 fails to start for any reason as for example dueto failure of the motor 13, the temperature of the thermal elementcontinues to rise due to radiation and the gravity circulation of theheated air upwardly through the duct 14- which also will cause the limitcontrol to operate shutting down the burner and preventing excessivetemperatures in the blower compartment 10.

In certain applications of horizontal type furnaces, either gas or oilfired, a problem similar to that of the downflow furnace also exists inregards to reverse air circulation from either forced or gravity flow.For example in the horizontal furnace shown in Fig. 2 the flow of forcedair is in a direction opposite to that of the natural or gravitycirculation as shown by the solid and broken arrows. In the structureshown in Fig. 2 equivalent elements have been given the same referencenume als since they perform the same functions. In fact the onlydifferences between the horizontal furnace of Fig. 2 and the verticalfurnace of Fig. l is in the relative horizontal positioning of theblower and heater.

The furnace of Fig. 2 when located for example in an attic may takeoutside air in through a grille 30 and under the operation of the blower4 force the air over the heater 1 and downwardly through a duct orgrillework 31. in the ceiling of the home. Since this outlet is at alower elevation than the inlet grille 30, the natural or gravity aircirculation is upwardly from the grille 31 through the heater and blowerand outwardly through the outside grille 30. The duct 14 is arranged ina relatively horizontal position with its outlet end 15 in communicationwith the blower compartment 10 and its inlet in communication with theheater compartment 11 so that under either forced or gravity circulationthe air passes through the duct 14 into the blower compartment 10. Henceunder either forced or gravity air circulation the control 17 operatesin the same manner as the control 17 of Fig. 1.

Like the vertical furnaces of Fig. 1, the downfiow horizontal furnacesof the type shown in Fig. 2 are subject to the problem of faultyoperation of fan and limit controls due to the fact that the circulationof air by gravity through the furnace is opposite to that caused byforced circulation. By positioning the duct in the path of either airflow with its outlet end terminating in the blower compartment, a singlefan and limit control switch will serve to control the operation of thefurnace under either normal or abnormal conditions.

While the present invention has been described with reference to certainspecific embodiments thereof, it will be understood that variousmodifications may be made by those skilled in the art without departingfrom the invention. The appended claims are therefore intended to coverall such modifications as come within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A downflow forced air furnace including a heater, means including ablower for circulating return air over said heater in a directionopposite to the normal gravity flow of air over said heater anddischarging the heated air into a space to be heated, a duct positionedin heat exchange relationship with the air surrounding said heaterhaving an outlet end communicating with the inlet to said blower and theother end open to the air being discharged into the space to be heatedso that air flow through said duct in the direction of the outlet endthereof is effected both by gravity circulation and by forcedcirculation during operation of said blower, and temperature responsivemeans for controlling the operation of said blower and said heater, saidtemperature responsive means being positioned adjacent the outlet end ofsaid duct in the path of air flowing through said duct.

2. A downflow forced air furnace including a heater, means including ablower for circulating air downwardly over said heater and dischargingthe heated air into a space to be heated, a duct in heat exchangerelationship with the air surrounding said heater having an upper outletend communicating with the inlet to said blower and the lower end opento the air being discharged into the space to be heated, and temperatureresponsive means for controlling the operation of said blower and saidheater, said temperature responsive means being positioned adjacent theoutlet end of said duct in the path of the air stream flowing throughsaid duct.

3. A downfiow forced air furnace includinga heater, a shell having anair inlet end and an air outlet end surrounding and spaced from saidheater, a blower compartment, a blower within said compartment having aninlet opening communicating with said compartment and a dischargeopening communicating with one end of said shell and means forcontrolling the operation of said furnace in response to the temperatureof the heater, said control means including a duct positioned in heatexchange relationship with the heater with one end of said ductterminating in said blower compartment and the other end in air flowrelationship with the air outlet end of said shell so that air fiowthrough said duct in the direction of the blower compartment end thereofis elfected both by gravity circulation and by forced circulation duringoperation of said blower and temperature responsive switching meansadjacent said one end of said duct in the path of air flowing throughsaid duct.

4. A downflow forced air furnace comprising a heating compartmentincluding a combustion chamber, a blower compartment, a blower withinsaid compartment having an inlet opening communicating with saidcompartment and a discharge opening communicating with one end of saidheating compartment to elfect a flow of forced air through said heatingcompartment in a direction opposite to that effected by gravitycirculation, and means for controlling the operation of said furnace inresponse to the temperature of the combustion chamber, said controlmeans including a duct in heat exchange relationship with saidcombustion chamber with one end in air flow relationship with thedischarge end of said heating compartment and the other endcommunicating with said blower compartment to discharge heated air intosaid blower compartment by both gravity and forced air circulation andtemperature responsive switching means adjacent the lower compartmentend of said duct in the path of air issuing from said duct.

5. A reverse flow heating system including a heater, means including ablower for forced circulation of air to be heated over said heater in adirection which is the reverse of the normal air flow over said heaterdue to gravity circulation, an air duct in heat exchange relationshipwith said heater, said duct having its outlet end communicating with theinlet end of said blower and its inlet end communicating with the heatedair which has been circulated over said heater whereby heated air isdischarged from its outlet end under both forced circulation and normalair flow conditions, and temperature responsive means responsive to thetemperature of heated air passing through the outlet end of said ductfor controlling the operation of said blower and said heater undereither forced or gravity air circulation.

6. A reverse flow heating system including a heater,

means including a blower for forced circulation of air to be heated oversaid heater in a direction which is the reverse of the normal air liowover said heater under gravity circulation, an air duct in heat exchangerelationship with said heater and having its upper outlet endcommunicating with the inlet of said blower and its lower inlet endcommunicating with the heated air which has been circulated over saidheater by said blower, and temperature responsive means in the path ofair flowing through the outlet end of said duct for controlling theoperation of said system under either forced or gravity air circulation.

7. A downfiow forced air heating system including a heater, a verticalshell surrounding said heater having an air inlet at the top thereof andan air discharge opening at the bottom, a blower compartment above saidshell, a blower in said compartment having its outlet connected to theinlet of said shell and its inlet within said compartment, a ductextending vertically in heat exchange relationship with the air withinsaid shell and having its upper end terminating in said blowercompartment in communication with said blower inlet and its lower end incommunication with the shell discharge opening where by heated airpasses upwardly through said duct both by gravity circulation and byforced circulation during operation of said blower, and means responsiveto the temperature of the heated air passing through the outlet end ofsaid duct for controlling the operation of said blower and said heater.

8. A downfiow forced air heating system including a heater, a verticalshell surrounding said heater having an air inlet at the top thereof andan air discharge opening at the bottom, a blower compartment above saidshell, a blower in said compartment having its outlet connected to theinlet of said shell and its inlet within said compartment, a ductextending vertically along and in contact with said shell in heatexchange relationship with said heater and having its upper endterminating in said blower compartment in communication with the blowerinlet and its lower end in communication with the shell dischargeopening whereby heated air passes upwardly through said duct both bygravity circulation and by forced circulation during operation of saidblower, and means positioned adjacent the blower end of said duct andresponsive to the temperature of the air issuing from said blower end ofsaid duct for controlling the operation of said blower and said heater.

Hellinan Feb. 6, 1945 Horn Apr. 22, 1952

